System and a method for improved crosshatch nanomachining of small high aspect three dimensional structures by creating alternating superficial surface channels

ABSTRACT

This invention provides the user the ability to accurately nanomachine surfaces with reduced tip induced errors. Nanomaching has two types of errors, a first type of error is brought about by the tip&#39;s shape and its aspect ratio. A second type of error due to the tip&#39;s deflection as it works the material. Therefore, embodiments of the present invention minimizes tip deflection errors allowing allow high aspect Nano-bits to reliably and accurately nanomachine small high aspect three dimensional structures to repair and rejuvenate photomasks

PRIORITY

This application claims benefit of provisional patent applications61/073,555, filed Jun. 18, 2008 and 61/073,561, filed Jun. 18, 2008.

FIELD OF THE INVENTION

This invention provides a user the ability to accurately nanomachine thesurface of a photomask with reduction of tip induced errors. Forexample, tip deflection errors are minimized allowing high aspectnano-bits to reliably and accurately nanomachine small high aspect threedimensional structures to repair and rejuvenate photomasks. The lifetimeof the nano-bits are also extended because the will be less strainplaced upon them in operation,

BACKGROUND OF THE INVENTION

The ability to machine structures of ever-decreasing dimensions isgoverned by many factors. One such factor is the material's atomicproperties with regard to its reduced dimensions. For example, workingat the nanometre scale, devices derive their properties from the wavenature of electrons and must be taken into account when machining. Anatomic force microscope (AFM) or scanning force microscope (SFM) is avery high-resolution type of scanning probe microscope commonly used toinvestigate nano-structures. It has a demonstrated resolution offractions of a nanometre, which is more than 1000 times better than theoptical diffraction limit. Information is gathered by “feeling” thesurface's atomic forces with a mechanical probe. Piezoelectric elementsfacilitate tiny, but extremely accurate and precise movements byelectronic or computer control.

The ability to repair photomasks and substrates at a nanometer scale isparticularly desirous and has been facilitated by the advent of the AFM.A photomask is an opaque plate with holes or transparencies that allowelectronic radiation energy, usually light to pass through in a definedpattern. They are commonly used in photolithography, which is a processused in micro fabrication of microprocessors to selectively remove partsof a thin film or the bulk of a substrate. It uses the electronicradiation energy to transfer a geometric pattern from a photomask to aelectromagnetic radiation sensitive chemical photo resist on thesubstrate. A series of chemical treatments then engraves the exposurepattern into the material underneath the photo resist. In a complexintegrated circuit, for example, a ComplementaryMetal-Oxide-Semiconductor (CMOS) wafer will go through thephotolithographic cycle up to 100 times and involve up to 100 photomask(one for each layer).

Moore's law describes a long-term trend in the history of computinghardware. Since the invention of the integrated circuit in 1958, thenumber of transistors that can be placed inexpensively on an integratedcircuit has increased exponentially, doubling approximately every twoyears The doubling was achieved mostly through the use of enhancedphotolithography techniques employing photomasks. Over the past fivedecades the wavelength of the light source has been reduced to permitsmaller feature size with photolithography, but the photomask complexityhas also increased. As a result, photomask designers need ways to ensurerepeatable and faithful reproduction of photomask's pattern onto thesubstrate. Therefore, the most critical issue for the production ofphotomasks is controlling and eliminating pattern defects in thephotomasks.

Integrated circuit designers are using methods calledReticle-enhancement techniques (RETs) to improve reproductionreliability and have been used along with various exposure approaches,such as double-patterning and extreme-ultraviolet (EUV) technologies.One RET is optical proximity correction (OPC), in which subresolutionchanges to the shape of a feature greatly improve its printability.Smaller, more subtle, and increasingly unavoidable defects in thephotomask's features can render expensive photomasks, or even an entiremask set worthless.

The types of defects on the photomask in need of removal includetrimming of unwanted carbon patches, the sequential defect removal ofgrowth particles and correcting irregularly shaped quartz bump defects.Currently, there are two options for photomask repair, Focused Ion Beam(FIB) or laser. While each technique has its advantages and uniquecapabilities, each has its particular limitations. Photomask repairtechnology has lagged well behind the capability requirements listed inthe International Technology Roadmap for Semiconductors (ITRS). The ITRSis a set of documents produced by a group of semiconductor industryexperts. These experts are representative of the sponsoringorganizations which include the Semiconductor Industry Associations ofthe US, Europe, Japan, Korea and Taiwan.

Additionally, the need for sub-wavelength resolution has driven theimplementation of phase-shifting photomasks for hyper-critical layerprocessing. The increased complexity of this layering technique has, inturn, dramatically increased photomask costs and cycle time. Advancedalternating phase shift photomasks may cost in excess of $10,000 perlayer and take five or six times as long to produce as a standardphotomask.

The production of even a single layer photomask for today's multicoremicroprocessors is a significantly difficult operation and the resultsare not always optimal. Additionally, the time to produce and qualitycheck a single layer photomask is long. If a layer of a photomask has tobe “reshot”, the time and cost both go up exponentially. The machinesthat produce the photomask are expensive, so a fabricator usuallyschedules their machine for continuous fabrication of many photomaskjobs to recover their costs. If a rewrite of a photomask must be done,it will have an adverse effects to the production schedule of thefabrication plant, which may miss deadlines and lose contracts.Therefore, it is extremely desirable to be able to repair any existingdefects on the photomask post production.

Repair of photomask defects is quickly becoming an in-linemask-production and maintenance necessity. This means the user of thephotomask does not have the time luxury to have a new set of photomaskcreated to replace a defective one. Even a miniscule defect on aphotomask will render a microprocessor produced with the defectivephotomask inoperable.

Material-subtractive repair technology nanomachining employs anapplication of atomic force microscopy (AFM). Nanomachining removes maskmaterial, such as opaque defects, with no chemical residuals andunsurpassed depth control. Past technical challenges included poorrepair-sidewall angles and poor shape definition in extremely small,high-aspect-ratio patterns. FIG. 1 illustrates the stress placed uponnanomaching tip 14 removing a defect 11 within a photomask 10. Thestress point 15 clearly illustrates the deformation of the nanomachingtip 14, which should be pryamidical. This shape is usually chosenbecause of its three sided cross sectional properties.

It is therefore desirable to have a method for fabricating precise highaspect ratio nanometer structures, especially to repair and rejuvenatephotomasks used in photolithography using nanomaching and atomic forcemicroscopy that ensures less nanomaching tip deflection, providesunsurpassed depth control and provides better sidewall shaping. Thepresent invention satisfies that need, as well as others, and overcomeslimitations in conventional fabrication methods.

SUMMARY OF THE INVENTION

The foregoing needs are met, to a great extent, by the presentinvention, wherein in one aspect a system and method are provided thatin some embodiments a method of repairing a defect region of a photomaskwith a first nanomaching tip of a probe affixed to a cantilever arm,said method comprising the steps of positioning said first nanomachingtip inwardly by a first offset from non defect region into said defectregion proximate to said surface region. Material is then removed fromsaid surface region using AFM by moving said first nanomaching tip in afirst direction and positioning said first nanomaching tip by a secondoffset distance from non defect region proximate to said surface regionand removing material from said surface region using AFM by moving saidfirst nanomaching tip in the opposite direction of the previous materialremoval direction. This is repeated while alternating first directionuntil said first probe reaches the non defect region of said photomask.More material is removed from said surface region using AFM by movingsaid first nanomaching tip in a second direction and repositioning saidfirst nanomaching tip by a third offset distance from non defect regionproximate to said surface region and removing material from said surfaceregion using AFM by moving said first nanomaching tip in the oppositedirection of the previous material removal direction. This is repeatedwhile alternating said second direction until said first probe reachesthe non defect region of said photomask. The above is repeated whileincreasing said first nanomaching tip 's depth until the defect regionis at a desired depth.

In an alternative embodiment, another method of repairing or modifying asurface region of a photomask with a first nanomaching tip of a probeaffixed to a cantilever arm consists of positioning said firstnanomaching tip near a surface of said photomask and removing perimetermaterial from said surface region using atomic force microscopy (AFM)while moving said first nanomaching tip in a differing directions aroundsaid surface region to form a perimeter channel. The tip is moved to afirst nanometre offset value from a first side of perimeter channel andmaterial is removed from said surface region using AFM while moving saidfirst nanomaching tip parallel to a first side of perimeter channel. Thetip is them moved again a second nanometre offset value distal from saidfirst side of perimeter channel and the above is repeated until firstprobe reaches an opposite perimeter channel. The tip is then moved athird nanometre offset value offset from a side adjacent to first sideof perimeter channel and more material is removed from said surfaceregion using AFM while moving said first nanomaching tip parallel tosaid side adjacent to first side of perimeter channel. The tip is movedagain another nanometre offset value offset from said side adjacent ofperimeter channel and the above is repeated until said first probereaches the opposite adjacent perimeter channel.

There has thus been outlined, rather broadly, certain embodiments of theinvention in order that the detailed description thereof herein may bebetter understood, and in order that the present contribution to the artmay be better appreciated. There are, of course, additional embodimentsof the invention that will be described below and which will form thesubject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of embodiments inaddition to those described and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein, as well as the abstract, are for thepurpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may more readily be understood, reference isdirected to the accompanying drawings.

FIG. 1 is an illustration of a nanomaching tool attached to an atomicforce microscope illustrating the stress placed upon a nanomachiningtip.

FIG. 2 is an illustration of a nanomaching tool attached to an atomicforce microscope after making a series of parallel material extractionson a photomask.

FIG. 3 is an illustration of the nanomaching tool attached to an atomicforce microscope after making a series of orthogonal materialextractions on the photomask.

FIG. 4 is an illustration of the photomask after an additional series ofparallel orthogonal material extractions

FIG. 5 is an illustration of the photomask after the AFM has removedmaterial.

FIG. 6 is an illustration of the nanomaching probe after making a firstpermitter pass.

FIG. 7 is an illustration of the nanomaching probe after making a secondpermitter pass.

FIG. 8 is an illustration of the nanomaching probe after making a thirdpermitter pass.

FIG. 9 is an illustration of the nanomaching probe after making a forthpermitter pass.

DETAILED DESCRIPTION

Detailed embodiments of the present invention are disclosed herein;however, it is to be understood that the disclosed embodiments aremerely illustrative of the invention that may be embodied in variousforms. In addition, each of the examples given in connection with thevarious embodiments of the invention are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

FIG. 2 illustrates an example of the method of a first embodiment of thepresent invention in which a photomask 10 is in need of opticalcorrection within a desired work area or defect region 13. A cantileverarm 12 of an atomic force microscope platform holds a first nanomachingtip 14. A first pass of individual parallel passes (cuts) 15-19 aresliced through the work area or defect region 13 at depths less than 30nanometres depending on the material of the photomask 10 and thecharacteristics of the first nanomaching tip 14.

The process begins by positioning the nanomaching tip 14 at thebeginning of a first pass 15. The nanomaching tip 14 is lifted andpositioned at the next parallel position. This technique minimizesprogressive tip deflection from material compression and debris pile-upwhich may accumulate as the material extraction process is carried out.After pass 15 is carried out, the nanomaching tip 14 is lifted andrepositioned and pass 16 is performed. After pass 16, the nanomachingtip 14 is lifted and pass 17 is performed. The iterative process iscontinued until all the parallel passes 15 through 19 are complete.

The next set of passes 20-24 as illustrated in FIG. 3 are similar to thefirst, except they are orthogonal to the parallel passes 20-24. Forexample, pass 20 is carried out, the nanomaching tip 14 is lifted andrepositioned and pass 21 is performed. After pass 21, the nanomachingtip 14 is lifted and pass 22 is performed. The process of incrementingthe index to the next pass is continued until all the parallel passes 20through 24 are complete.

The alternating sequence of orthogonal passes can be repeated until adesired depth of the work area or defect region 13 is achieved leavingan orthogonal series of isolated channels defining the boundaries of therepair while leaving a grid of small isolated pillars 30 on the surfaceof the work area or defect region 13. The small isolated pillars 30, asshown in FIG. 4, can be made smooth with the nanomaching tip 14 or withan additional tip or tips, depending on the precision required and afinished repair is shown in FIG. 5. The additional tips, with adiffering aspect ratios or differencing composite material can be usedto “smooth” out or polish the bottom of the desired work area or defectregion 13.

In an alternative embodiment, a next series of passes would beperformed, but the nanomaching tip 14 would be offset from its first setof passes. For example, the nanomaching tip 14 is directed to perform aseries of passes that would traverse through the center of the pillars30, paralleling the channels “cut” from a previous pass, permitting afiner control of the debris removal.

In yet another embodiment, one or more sets of orthogonal passes of thenanomaching tip 14 is performed, but at an ever increasing depths untila desired depth is achieved. This embodiment removes the material indiscrete depth levels. The nanomaching tip 14 can also be changed to adifferent nanomaching tip with differing aspect ratios or physicalcharacteristics to assist with the removal of the undesired material.

In another embodiment, the perimeter of the work area or defect region13 is first “carved out” before the orthogonal crosshatching of aprevious embodiment is performed. An advantage of this embodiment isthat is helps preserves the desired shape's fidelity. This is achievedby minimizing the amount of material displaced in producing the pillars(orthogonal cuts) and yet still defines the repair area for thesubsequent debris removal. The present embodiment also minimizes thepotential of accumulating repair debris which would deflect thenanomaching tip 14 from accurately defining the repair shape. Theperimeter could be used as a repository for any removed material, thushelping keep the nanomaching tip 14 clean of any debris which couldcause drag or jumping ahead deflections which could impede thenanomaching tip's ability to traverse in a straight cutting vector. Theperimeter also greatly reduces or eliminates lateral deflection whenmaking parallel cuts, because it helps prevent drag or jumping aheaddeflections when performing the cut's in the parallel direction.Additional subsequent cuts would be preferentially deflected into theprior seed cuts resulting in a self-aligning repair process.

For example, referring to FIGS. 6-9, a first pass 42 of the nanomachingtip 14 defines a first portion of perimeter of the work area or defectregion 13. A second pass 44, a third cut 46 and a fourth cut 48 completethe scribing of the perimeter. The perimeter cutting process may berepeated if deeper work area is preferred, usually to within 0-20nanometers of a desired depth. The steps of the first embodiment may beperformed to remove the material from the work area or defect region 13.In a preferred embodiment, the user may lift the nanomaching tip 14between each perimeter cut. But, in an alternative embodiment, the usercould practice the invention without lifting the nanomaching tip 14between each perimeter cut.

In another embodiment, the perimeter cuts can be at differing offsets.The user could progressively increase the depth of the cuts at each asthe nanomaching tip 14 works it way around the perimeter. The increaseof the depth's cut could be increased after each complete perimeter passor it could be increased after each cut before the direction is changedor it could be gradually increased throughout the entire perimetercutting.

For other embodiments the sequence and directions of the cuts can becontrolled to enhance the shape of the repair or by the characteristicsof the material being nanomachined. For example, indents start at theworst-resolved corners with the separated cuts moving towards thebest-resolved corners.

Finally, it is to be understood that various alterations, modificationsand/or additions may be introduced into the constructions andarrangements of parts previously described without departing from thespirit or ambit of the invention.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

1. A method of repairing a defect region of a photomask with ananomaching tip of a probe affixed to a cantilever arm, said methodcomprising the steps of: (A) positioning said first nanomaching tipinwardly by a first offset from non defect region into said defectregion proximate to said surface region; (B) removing material from saidsurface region using AFM by moving said first nanomaching tip in a firstdirection; (C) positioning said first nanomaching tip by a second offsetdistance from non defect region proximate to said surface region andremoving material from said surface region using AFM by moving saidfirst nanomaching tip in the opposite direction of the previous materialremoval direction; (D) repeating step C while alternating firstdirection until said first probe reaches the non defect region of saidphotomask; (E) removing material from said surface region using AFM bymoving said first nanomaching tip in a second direction; (F) positioningsaid first nanomaching tip by a third offset distance from non defectregion proximate to said surface region and removing material from saidsurface region using AFM by moving said first nanomaching tip in theopposite direction of the previous material removal direction; (G)repeating step F while alternating said second direction until saidfirst probe reaches the non defect region of said photomask; (H)repeating steps C through F while increasing said first nanomaching tip's depth until the defect region is at a desired depth.
 2. The method ofclaim 1, wherein the first direction and the second direction areorthogonal.
 3. The method of claim 1, wherein first offset distance andthe second offset distance is selected by said first nanomaching tipcharacteristics.
 4. The method of claim 1, wherein first offset distanceselected from the range of 1 nanometres to 20 nanometres.
 5. The methodof claim 1, wherein second offset distance selected from the range of 1nanometres to 20 nanometres.
 6. The method of claim 1, wherein thirdoffset distance selected from the range of 1 nanometres to 10nanometres.
 7. The method of claim 1, wherein said first nanomaching tipis replaced with a second tip with differing characteristics.
 8. Themethod of claim 5, wherein said second tip is replaced with a third tipwith differing characteristics.
 9. The method of claim 1, wherein atstep G said second offset distance is one-half of the previous value.10. The method of claim 1, wherein at step G said third offset distanceis one-half of the previous value.
 11. A method of repairing ormodifying a surface region of a photomask with a first nanomaching tipof a probe affixed to a cantilever arm, said method comprising the stepsof: (A) positioning said first nanomaching tip near a surface of saidphotomask; (B) removing perimeter material from said surface regionusing atomic force microscopy (AFM) while moving said first nanomachingtip in a differing directions around said surface region to form aperimeter channel; (C) moving said first nanomaching tip approximately2-10 nanometres offset from a first side of perimeter channel; (D)removing material from said surface region using AFM while moving sadfirst nanomaching tip parallel to a first side of perimeter channel; (E)moving said first nanomaching tip another approximate 2 to 10 nanometresdistance from said first side of perimeter channel; (F) repeating stepsD and E until said first probe reaches an opposite perimeter channel;(G) moving said first nanomaching tip approximately 2 to 10 nanometresoffset from a side adjacent to first side of perimeter channel; (H)removing material from said surface region using AFM while moving saidfirst nanomaching tip parallel to said side adjacent to first side ofperimeter channel; (I) moving said first nanomaching tip anotherapproximate 2 to 10 nanometres offset from said side adjacent ofperimeter channel; and (J) repeating steps H and I until said firstprobe reaches the opposite adjacent perimeter channel.
 12. The method ofclaim 1, wherein step B is repeated until the depth of the perimeter iswithin 2 to 30 nanometres of a final depth;
 13. The method of claim 1,wherein steps C through J are repeated until the depth of the surfaceregion is within 2 to 30 nanometres of the final depth;
 14. The methodof claim 1, wherein the steps of C through J are repeated with theoffsets in steps H and J are in the 2 to 10 nanometre range.
 15. Themethod of claim 4, wherein the steps of C through J are repeated untilthe depth of the surface region is at the final depth
 16. The method ofclaim 4, wherein the steps of C through J are repeated with a second tipuntil the depth of the surface region is at the final depth